Turning substrates from electron-poor to electron-rich for nonsacrificial aerobic hydroxylation under visible light

Aerobic oxidation of arylboronic acids under visible light has been intensively explored for synthesis of phenols, for which the need for sacrificial electron-donor agents detracts from the benignancy and sustainability. Here we present the first demonstration of nonsacrificial photocatalytic hydroxylation of arylboronic acids. By turning the electron-poor substrates to electron-rich, the photocatalytic aerobic oxidation proceeds through a mechanism completely different from previous ones, involving the direct oxidation of the aryl-B substrates to aryl radicals through visible-light-induced single-electron transfer to photocatalysts. The protocol not only obviates the need for sacrificial electron donors but also allows efficient reactions in water. It is applicable to various photocatalysts, either homogeneous or heterogeneous. The work provides a green alternative to the traditional methods for synthesis of phenols, and the insight gained from it may open new perspectives for organic photosynthesis that involve aryl radicals.